#! /usr/bin/env python
# -*- coding: utf-8 -*-
# vim:fenc=utf-8
#
# Copyright © 2018 crane <crane@his-pc>
#
# Distributed under terms of the MIT license.

"""

"""


class Solution:
    """
    相同的数异或得0
    任何数与0异或的本身
    异或具有交换性
    """
    def singleNumber(self, A):
        end = 0
        for i in A:
            end ^= i

        return end


def main():
    print("start main")

if __name__ == "__main__":
    main()
